Crystal structure of alluaudite-type Na₄Co(MoO₄)₃

The title compound, tetra­sodium cobalt(II) tris­[molyb­date(IV)], was prepared by solid-state reactions. The structure is isotypic with Na₃In₂(AsO₄)₃ and Na₃In₂(PO₄)₃. The main structural feature is the presence of infinite chains of edge-sharing X₂O₁₀ (X = Co/Na) dimers, which are linked by MoO₄ tetra­hedra, forming a three-dimensional framework enclosing two types of hexa­gonal tunnels in which Na⁺ cations reside. In this alluaudite structure, Co and Na atoms are located at the same general site with occupancies of 0.503 (5) and 0.497 (6), respectively. The other three Na and one of the two Mo atoms lie on special positions (site symmetries 2, -1, 2 and 2, respectively). The structure is compared with similar structures and other members of alluaudite family.